1. Field of the Invention
The present invention relates to a manufacturing method for a semiconductor device.
2. Description of the Background Art
Miniaturization in a lithographic technology has progressed by using light for exposure with a shorter wavelength and increasing the numerical aperture (NA value) of the imaging optical system in a stepper. Specifically, the wavelength of light for exposure has been shortened from the I line (wavelength: 365 nm), to the KrF excimer laser beam (wavelength: 248 nm), and then to the ArF excimer laser beam (wavelength: 193 nm). In addition, the NA value has gradually increased up to a value of approximately 0.9, and furthermore, an NA value of 1 or greater has been realized by filling up the space between the projection lens and the substrate with water so that the space soaks up a liquid.
In response to the above, according to the roadmap for progressing further miniaturization, the minimum pitch used for semiconductor devices has become such that hp (half pitch): 65 nm→hp: 45 nm→hp: 32 nm in order to reduce the dimensions of the pattern. Here, two mass production tools for transcribing a pattern with hp: 32 nm, exposure to EUV light, and exposure to ArF light with the space between the projection lens and the substrate soaked with a liquid are considered to be promising. However, it is considered that the unit for mass production for exposure to EUV light will not be made by the time mass production starts, judging from the schedule for developing a device, and therefore, it is examined that exposure to ArF light with the space between the projection lens and the substrate soaked with a liquid is kept being used and applied. It is considered that the maximum limit of the NA value using water (index of refraction: 1.43) as the liquid with which the space is soaked is 1.3 to 1.35, and the theoretical limit value of the minimum pitch that can be transcribed with this NA value is K1×wavelength/NA=0.25×193/1.35=35.7 nm, and thus, patterns with hp: 32 nm cannot be transcribed.
In addition, location patterns with the minimum pitch are formed under such processing conditions that the pitch is no less than approximately 0.35 when calculated as a k1 factor (here, k1 is a process factor) in accordance with a conventional SOC process, while patterns with a minimum pattern pitch of 90 nm of which the application is examined for the wire layers of hp 32 nm node SOC are formed under such processing conditions that k1=approximately 0.3 close to the theoretical limit value k1=0.25 due to the stepper that can be applied, and it becomes very difficult to build a pattern in an arbitrary form, for example a logic wiring pattern, under such process conditions that k1=approximately 0.3.
In these circumstances, exposure to ArF light with the space between the projection lens and the substrate soaked with a liquid+double patterning technology is examined as a lithographic technology corresponding to 32 nm node SOC. That is to say, a pattern transcription method is examined, where the mask pattern is divided into a number of patterns so that the pattern pitch of the desired circuit pattern to be transcribed onto a substrate need not be so precise as when patterns are formed under such processing conditions that k1=approximately 0.35, and the divided mask patterns are exposed to light through multiple exposure, or multiple processing is carried out on the divided mask patterns.
Specifically, a method is examined where when pattern arrangements in an arbitrary form, for example wiring patterns of SOC, are presupposed, in the case where, k1>approximately 0.35 in the formula CD=k1×wavelength of light for exposure/NA (here, CD is the resolution and NA is the numeric aperture) for the resolution, the pitch in the pattern arrangement is CD×2 or greater, making transcription possible through one-time exposure to light, even when the pattern is not divided, while in the case of k1<approximately 0.35, it becomes more difficult to transcribe a pattern where the pitch in the arrangement of the pattern is than CD×2 or more through one-time exposure to light, and therefore, the mask pattern is divided so that the pitch in the pattern arrangement need not be so precise.
In addition, there are several methods in a pattern dividing method in accordance with the double patterning method, and there are methods according to which a pattern is divided into two masks in such a manner that every other line thinned out in a periodic pattern of an arrangement with high density, as described above, and the mask pattern is divided in two, one for the components in the direction x and the other for the components in the direction y, in the case where two-dimensional circuit patterns are arranged with high density in the same layer. As for these divided mask patterns, a desired pattern can be formed through multiple exposure to light or multiple processing, for example exposure to light→processing→exposure to light→processing.
As such a pattern transcription method, there is a method according to which a pattern figure with the pitch of the resolution limit or smaller is divided so that the arrangement makes it so that the pitch need not be so precise up to the level that the pattern can be resolved. In the case where a pattern with 32 mL/S (hp=32 nm), which is finer than the theoretical resolution limit value hp=37 nm, is processed under such conditions that ArF light is used with NA=1.20, for example, the mask pattern is divided in two with a line of 32 nm and a pitch of 128 nm by removing every other line. This is used for multiple exposure to light and multiple processing, and thus, a desired pattern is formed (see for example SEMATECH Litho Forum 2006 conference proceedings, Proceedings of SPIE 2005, vol. 5754-32, Proceedings of SPIE 2006, vol. 5754-203 and Proceedings of SPIE 2006, vol. 6154-37).
In addition, there is a multiple exposure to light method using an electron beam exposure method according to which a portion where lines are bent in the pattern is used as a border for division and a double exposure portion is provided in acute angle portions from among portions where lines are bent in the pattern, or a non-exposure portion is provided in obtuse angle portions for correction, and thus, a desired pattern is formed (see for example Japanese Patent Application Laid-Open No. 11 (1999)-135417).
In accordance with pattern transcription methods using a conventional double patterning method, whether or not the mask pattern is divided is determined on the basis of the density of the pattern inside the same layer. That is to say, patterns of which the density is so high as to be difficult or impossible to transcribe through one-time exposure to light, for example patterns with hp 32 nm, are divided for multiple exposure to light or multiple processing, while patterns with a low density are not divided, and transcribed through one-time exposure to light.
Due to the nature of pattern formation, however, corner portions are rounded due to the intensity of light when a pattern including two adjacent sides forming a corner portion is transcribed onto a substrate through one-time exposure to light. For example, in the case where an active region pattern which forms a rectangular corner portion and a gate pattern above an activation pattern and in the vicinity of the corner portion are arranged in a similar relationship between an active region pattern and a gate pattern in a MOS transistor, the active region having a low pattern density is transcribed through one-time exposure to light, and the corner of the active region pattern is rounded. The gate pattern is positioned against the corner portion of the active region pattern for overlapping processes, and therefore, when the corners of the active pattern are rounded, causing the location of the gate pattern to shift, a problem arises, such that the properties of the transistors fluctuate. As a technique for preventing the corner portions from being rounded as described above, there is a technology for correction through optical proximity effects, but there is a limit in terms of prevention of rounding using this method.
In addition, although in order to secure a margin for inconsistency in the properties of the transistors, measures are taken by securing an extra margin for the operation, and arranging the transistors in the layout at a sufficient distance to such a degree that there is no inconsistency in terms of the properties, these measures have problems, such that the properties of the chip deteriorate and the area of the chip expands.
In addition, in accordance with a multiple exposure method using an electron beam method, a mask with a complex form must be used, in order to correct the amount of dosage of electrons, due to the proximity effect, and it is assumed that no hard mask is used, and therefore, a problem arises with the precision in the mask arrangement and cost.